rtc: remove v3020 driver

The v3020 RTC driver was exclusively used by the now removed
cm-x300.c machine.

Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>
Cc: linux-kernel@vger.kernel.org
Cc: linux-rtc@vger.kernel.org
Acked-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>